Methods for encoding/decoding of video using common merging candidate set of asymmetric partitions

ABSTRACT

The present invention provides video encoding and decoding methods using block merging, which can be applied to a high resolution video of more than HD (High Definition) resolution. A video encoding method includes partitioning a current block into a first and a second prediction unit by using asymmetric partitioning, constructing a list of common merging candidate blocks including a predetermined number of common merging candidate blocks selected from adjacent blocks of the current block, selecting at least one candidate block from among the list of common merging candidate blocks and sending information of the selected candidate block to a decoder for each of the first and the second prediction unit.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 13/683,771, filed on Nov. 21, 2012. Further, this applicationclaims the priorities of Korean Patent Application No. 10-2011-0123209,filed on Nov. 23, 2011; and No. 10-2012-0016616, filed on Feb. 17, 2012in the KIPO (Korean Intellectual Property Office), the disclosure ofwhich are incorporated herein in their entirety by reference.

BACKGROUND

1. Technical Field

The present invention relates to encoding and decoding of video and morespecifically, video encoding methods, video encoding apparatuses, videodecoding methods, and video decoding apparatuses by using block merging.

2. Description of the Related Art

Conventional video compression uses inter prediction and intraprediction techniques designed to remove redundancy between pictures forimproving compression efficiency.

Video encoding algorithms based on intra prediction compress a video byremoving temporal redundancy between pictures, where motion compensatedinter-frame prediction is a typical technique for this purpose.

Motion compensated inter-frame prediction technique generates a motionvector by searching at least one reference picture located before and/orafter a current encoding picture for a region similar to a currentencoding block. It applies DCT (Discrete Cosine Transform) to residuesbetween the current block and a prediction block obtained from motioncompensation by using the generated motion vector. The result of DCT istransmitted after quantization and entropy encoding.

In case of motion compensated inter prediction, motion vector isgenerated by dividing a picture into a plurality of blocks having apredetermined size and motion compensation is performed by using thegenerated motion vector. Individual motion parameters for the respectiveprediction blocks obtained from motion compensation are transmitted to adecoder.

SUMMARY

Since the number of blocks per picture increases in case of highresolution video of more than HD (High Definition) resolution, it is notdesirable in the respect of coding efficiency to transmit motionparameters to a decoder for each prediction block as the amount ofmotion parameters transmitted becomes considerably large.

Example embodiments of the present invention provides video encodingmethods and video encoding apparatuses using block merging which can beapplied for high resolution videos of more than HD (High Definition)resolution.

Example embodiments of the present invention also provides videodecoding methods and video decoding apparatuses using block mergingwhich can be applied for high resolution videos of more than HDresolution.

In some example embodiments, an encoding method according to one exampleembodiment of the present invention includes constructing a list ofcommon merging candidate blocks including a predetermined number ofcommon merging candidate blocks selected from among adjacent blocks of acurrent coding unit asymmetrically partitioned into a first and a secondprediction unit; and selecting at least one candidate block from amongthe list of common merging candidate blocks for each of the first andthe second prediction unit and sending information of the selectedcandidate block to a decoder for each of the first and the secondprediction unit. The list of common merging candidate blocks may includecommonly used merging candidate blocks in case block merging isperformed for the first and the second prediction unit. The blockmerging can be performed only when the size of the current coding unitis 8-by-8. The largest coding unit (LCU) may be divided into a pluralityof non-overlapping motion estimation regions. Motion estimation may beperformed sequentially on the motion estimation regions within thelargest coding unit. The motion estimation can be performed in aparallel fashion for all prediction units belonging to a motionestimation region within the largest coding unit (LCU). According to thesize of the motion estimation region, whether to allow parallel mergingfor prediction units within the motion estimation region by using thecommon merging candidate blocks can be determined. The parallel mergingfor all the prediction units within the motion estimation region may beallowed only when the size of the motion estimation region is largerthan a predetermined size. To indicate possibility of processing of theparallel merging according to the size of the motion estimation region,a predetermined value according to the size of the motion estimationregion may be transmitted in a PPS (Picture Parameter Set) from anencoder to the decoder. In case the current prediction unit and aprediction unit adjacent to the current prediction unit belong to thesame motion estimation region, the corresponding adjacent predictionunit is denoted as non-available, whereas in case the current predictionunit and the prediction unit adjacent to the current prediction unitbelong to motion estimation regions different from each other, thecorresponding adjacent prediction unit is denoted as available. The listof common merging candidate blocks may include a spatial mergingcandidate block and a temporal merging candidate block. The first andthe second prediction unit within the current coding unit utilize areference picture index of a block, at a predetermined particularposition, from among spatial common merging candidate blocks as areference picture index for temporal motion vector prediction (MVP) ofthe temporal merging candidate block. The block, at the predeterminedparticular position, can be rendered executable through parallelprocessing by using previously encoded adjacent block which can beconstructed even before reconstructing a motion parameter of a first PU0and a second prediction unit PU1 from among blocks included in the listof common merging candidate blocks. The common merging candidate blockscan be predetermined beforehand according to a rule between the encoderand the decoder.

In other example embodiments, an encoding apparatus includes an interprediction unit configured to construct a list of common mergingcandidate blocks including a predetermined number of common mergingcandidate blocks selected from blocks adjacent to a current coding unit,which have been asymmetrically partitioned into a first and a secondprediction unit; and configured to select at least one candidate blockfrom the list of common merging candidate blocks for each of the firstand the second prediction unit.

In still other example embodiments, a decoding method according to oneexample embodiment of the present invention includes constructing a listof common merging candidate blocks including a predetermined number ofcommon merging candidate blocks selected from among adjacent blocks of acurrent coding unit asymmetrically partitioned into a first and a secondprediction unit; generating a motion vector on a block basis byreconstructing a motion parameter of a block-merged block by using atleast one candidate block selected from the list of common mergingcandidate blocks for each of the first and the second prediction unit;and performing motion compensation by using the generated motion vectorand a reference picture. The common merging candidate blocks of thesecond prediction unit consist only of adjacent blocks which can beconstructed before a motion parameter of the first prediction unit isreconstructed. The block merging can be performed only when the size ofthe current coding unit is 8-by-8. The largest coding unit (LCU) may bedivided into a plurality of non-overlapping motion estimation regions.Motion estimation may be performed sequentially on the motion estimationregions within the largest coding unit. The motion estimation can beperformed in a parallel fashion for all prediction units belonging to aestimation region within the largest coding unit (LCU). According to thesize of the motion estimation region, whether to allow a parallelmerging for prediction units within the motion estimation region byusing the common merging candidate blocks can be determined. Theparallel merging for all the prediction units within the motionestimation region is allowed only when the size of the motion estimationregion is larger than a predetermined size. In case the currentprediction unit and a prediction unit adjacent to the current predictionunit belong to the same motion estimation region, the correspondingadjacent prediction unit is denoted as non-available, whereas in casethe current prediction unit and the prediction unit adjacent to thecurrent prediction unit belong to motion estimation regions differentfrom each other, the corresponding adjacent prediction unit is denotedas available. The list of common merging candidate blocks may include aspatial merging candidate block and a temporal merging candidate block.The first and the second prediction unit within the current coding unitutilize a reference picture index of a block, at a predeterminedparticular position, from among spatial common merging candidate blocksas a reference picture index for temporal motion vector prediction (MVP)of the temporal merging candidate block. The block, at the predeterminedparticular position, can be rendered executable through parallelprocessing by using previously encoded adjacent blocks which can beconstructed even before reconstructing a motion parameter of a first PU0and a second prediction unit PU1 from among blocks included in the listof common merging candidate blocks.

In still other example embodiments, includes an inter prediction unitconfigured to construct a list of common merging candidate blocksincluding a predetermined number of common merging candidate blocksselected from blocks adjacent to a current coding unit asymmetricallypartitioned into a first and a second prediction unit; configured togenerate a motion vector on a block basis by reconstructing a motionparameter of a block-merged block by using at least one candidate blockselected from the list of common merging candidate blocks for each ofthe first and the second prediction unit; and configured to performmotion compensation by using the generated motion vector and a referencepicture.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the present invention will become more apparentby describing in detail example embodiments of the present inventionwith reference to the accompanying drawings, in which:

FIG. 1 illustrates symmetric partitioning;

FIG. 2 illustrates asymmetric partitioning;

FIG. 3 illustrates block merging of partitioned blocks in case aprediction unit (PU) having size of 2N×2N is partitioned into two N×2Nblocks in a vertical direction;

FIG. 4 illustrates a process where block merging of the two partitionedblocks of FIG. 3 and an encoding (or decoding) operation are performed;

FIGS. 5 to 7 illustrate common merging candidate blocks enablingparallel processing of prediction units PU0, PU1 partitionedasymmetrically according to example embodiments of the presentinvention;

FIG. 8 illustrates a process where block merging of two partitionedblocks in a parallel fashion and an encoding (or decoding) operation areperformed;

FIG. 9 is a block diagram of a video encoding apparatus using blockmerging according to one example embodiment of the present invention;and

FIG. 10 is a flow diagram illustrating a video encoding method usingblock merging according to one example embodiment of the presentinvention.

DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE PRESENT INVENTION

Example embodiments of the present invention can be modified in variousways and various example embodiments of the present invention can berealized; thus, this document illustrates particular example embodimentsin the appended drawings and detailed description of the exampleembodiment will be provided.

However, that is not meant for limiting the present invention to theparticular example embodiments; rather, it should be understood toinclude every possible modification, equivalent, or substitute of thepresent invention which belongs to the technical principles and scope ofthe present invention.

Terms such as first, second, and so on can be used for describingvarious components but the components should not be limited by theterms. The terms are introduced only for the purpose of distinguishingone component from the others. For example, a first component may becalled a second component without departing from the scope of thepresent invention and vice versa. The term of and/or indicates acombination of a plurality of related items described or any one of aplurality of related items described.

If a component is said to be “linked” or “connected” to a differentcomponent, the component may be directly linked or connected to thedifferent component but a third component may exist to connect the twocomponents even though the two components may be connected directly. Onthe other hand, if a component is said to be “linked directly” or“connected directly” to another component, it should be interpreted thatthere is no further component between the two components.

Terms used in this document have been introduced only to describeparticular example embodiment, not intended to limit the scope of thepresent invention. Singular expression should be interpreted to includeplural expressions unless otherwise stated explicitly. Terms such as“include” or “have” are meant to signify existence of embodiedcharacteristics, numbers, steps, behavior, components, modules, andcombinations thereof, which should be understood that possibility ofexistence or addition of one or more characteristics, numbers, steps,behavior, components, modules, and combinations thereof are notprecluded beforehand.

Unless otherwise defined, all the terms used in this document, whetherthey are technical or scientific, possess the same meaning as understoodby those skilled in the art to which the present invention belongs. Theterms such as those defined in a dictionary for general use should beinterpreted to carry the same contextual meaning in the relatedtechnology and they should not be interpreted to possess an ideal orexcessively formal meaning.

It should also be noted that in some alternative implementations, thefunctions/acts noted in the blocks may occur out of the order noted inthe flowcharts. For example, two blocks shown in succession may in factbe executed substantially concurrently or the blocks may sometimes beexecuted in the reverse order, depending upon the functionality/actsinvolved.

In what follows, with reference to appended drawings, preferredembodiments of the present invention will be described in more detail.For the purpose of overall understanding of the present invention, thesame components of the drawings use the same reference symbols andrepeated descriptions for the same components will be omitted.

In one example embodiment of the present invention, encoding anddecoding are performed by using recursive coding unit structure toaccommodate videos of more than HD (High Definition) resolution.

First, to describe the recursive coding unit structure, it is assumedthat each coding unit (CU) is square-shaped and each coding unit (CU)has a variable size of 2N×2N (where the size unit is pixel). Interprediction, intra prediction, transform, quantization, and entropyencoding may be performed on a CU basis.

The size of a coding unit (LCU) can be represented by powers of two,ranging from 8×8 to 64×64. The coding unit (CU) includes the largestcoding unit (LCU) and the smallest coding unit (SCU); for example, theLCU has the size of 64×64 whereas the SCU has the size of 8×8.

The coding unit (CU) has a recursive tree structure. For example, thesize 2N0 of one side of the largest coding unit CU0 may be 64 (N0=32)and the largest layer level or layer depth may be 4. A recursivestructure may be represented by using a series of flags. For example, incase the flag value of a coding unit (CUk) is 0 and layer level or layerdepth of the coding unit is k, coding for the coding unit (CUk) isperformed on a current layer level or depth. In case the flag value is1, the coding unit (CUk) whose current layer level or depth is k ispartitioned into four independent coding units (CUk+1). The layer levelor depth of the partitioned coding unit (CUk+1) becomes k+1 and the sizeof the coding unit (CUk+1) becomes (Nk+1)×(Nk+1). In this case thecoding unit (CUk+1) can be represented as a sub-coding unit of thecoding unit CUk. The coding unit (CUk+1) is processed recursively untilthe layer level or depth of the coding unit (CUk+1) reaches the maximumallowable layer level or depth. If layer level or depth of the codingunit (CUk+1) is the same as the maximum allowable layer level or depth,further partitioning is not allowed.

If the hierarchical splitting process as described above is completed,inter prediction or intra prediction is performed for terminal nodes ofthe coding unit hierarchy tree without further splitting, where theterminal coding unit is used as a prediction unit (PU), which is a baseunit for inter prediction or intra prediction.

The terminal coding unit is now partitioned to carry out interprediction or intra prediction. In other words, partitioning isperformed on a prediction unit. Here, a prediction unit (PU) representsthe base unit for inter prediction or intra prediction. In other words,a prediction unit is obtained as a terminal node of a coding unithierarchy tree after the hierarchical splitting process is completed; inother words, size of the prediction unit can take one of 64×64, 32×32,16×16, and 8×8.

One coding unit (CU), to carry out inter prediction or intra prediction,can be partitioned into prediction units. More specifically, a 2N×2Ncoding unit can be symmetrically partitioned along horizontal orvertical direction.

FIG. 1 illustrates symmetric partitioning. FIG. 1 assumes that size of acoding unit (CU) is 2N×2N (where N is a natural number and representedby pixel units).

With reference to FIG. 1, in case the prediction mode is interprediction, a 2N×2N coding unit P01 is symmetrically partitioned inhorizontal direction to perform the inter prediction, being partitionedinto a partition PU0 (P02b) having size of 2N×N and a partition PU1(P02a) having size of 2N×N; or a partition PU0 (P03a) of N×2N and apartition PU1 (P03b) of N×2N; or N×N partition PU0 (P04a), PU1, PU2, andPU3.

FIG. 2 illustrates asymmetric partitioning. FIG. 2 assumes that size ofa coding unit (CU) 2N×2N (where N is a natural number and represented bypixel units).

With reference to FIG. 2, in case the prediction mode is interprediction, a 2N×2N coding unit is asymmetrically partitioned inhorizontal direction to perform the inter prediction, being partitionedinto a partition PU0 (P11a) having size of 2N×nU (where nU is 2N×¼) anda partition PU1 (P12a) having size of 2N×nU (where nU is 2N×¾).Similarly, the 2N×2N coding unit can be asymmetrically partitioned invertical direction, being partitioned into a partition PU0 (P13a) havingsize of nL×2N (where nL is 2N×¼) and a partition PU1 (P23a) having sizeof nR×2N (where nR is 2N×¾); or a partition PU0 (P14a) having size ofnL×2N (where nL is 2N×¾) and a partition PU1 (P24a) having size of NR×2N(where nR is 2N×¼).

All the information including motion parameters (a motion vector, adifference value of a motion vector, a reference picture index, areference picture list, and so on) related to inter prediction istransmitted to a prediction unit, which is a base unit for interprediction, or a decoder for each of the partitioned prediction units.

In case of a video having more than HD (High Definition) resolution, thenumber of prediction blocks per picture (prediction unit partitioned ornot partitioned) increases; therefore, if motion parameters aretransmitted to a decoder for each of prediction blocks (predictionblocks partitioned or not partitioned), the amount of motion parametersto be transmitted gets significantly large, which is not desirable withrespect to coding efficiency and therefore a method for improving thecoding efficiency is needed.

To solve the problem described above, inter-frame encoding may beperformed by using block merging. Block merging is a technique intendedfor improving coding efficiency. In case blocks adjacent to a currentblock (or prediction unit) encoded prior to the current block have thesame motion parameter (a motion vector, a difference value of the motionvector, a reference picture index, a reference picture list, and so on)as that of the current block X, the adjacent blocks having the samemotion parameter as that of the current block X are merged with thecurrent block. Since the same motion parameter of the merged blocks istransmitted to a decoder, the amount of motion parameters to betransmitted to the decoder may be reduced without separatelytransmitting the motion parameter of the current block, and thus codingefficiency may be improved.

For example, in case a picture is split down to a terminal coding unitin the hierarchy, namely, the smallest coding unit (SCU) and a currentblock (prediction unit) X, which is the SCU, has the same motion vectoras a left-side adjacent block A0 and an upper-side adjacent block B0encoded previously, block A0, B0, and X are merged and transmitted to adecoder as having the same motion parameters. Here, the motionparameters include a motion vector, a difference value of the motionvector, a reference picture index, a reference picture list, and so on.In this case, a merging flag indicating whether block merging has beenapplied or not can be transmitted to the decoder.

FIG. 3 illustrates block merging of partitioned blocks in case aprediction unit (PU) having size of 2N×2N is partitioned into two N×2Nblocks in a vertical direction. FIG. 4 illustrates a process where blockmerging of the two partitioned blocks of FIG. 3 and an encoding (ordecoding) operation are performed.

With reference to FIG. 3, a 2N×2N coding unit (CU) is partitioned into apartition block PU0 having size of 2N×N and a partition block PU1 havingsize of 2N×N.

In what follows, a partitioned block denotes a partitioned predictionunit, functioning as a prediction unit. In the following, PU0 of FIG. 3is called a first prediction unit while PU1 of FIG. 3 is called a secondprediction unit.

In the following, adjacent blocks bordering the left-side boundary of apartition block (prediction unit) are called left-side adjacent blocks.In the left-hand side of FIG. 3, in case of a first prediction unit PU0filled with oblique lines, A1 belongs to the left-side adjacent blockswhile in the right-hand side of FIG. 3, in case of a second predictionunit PU1 filled with oblique lines, A1 belongs to the left-side adjacentblocks. For the first prediction unit PU0 oblique-lined in the left-handside of FIG. 3, A0 is a block bordering a bottom-side boundary of anadjacent block A1, which is called a bottom-side extension adjacentblock while, for the second prediction unit PU1 oblique-lined in theright-hand side of FIG. 3, A0 is a block bordering a bottom-sideboundary of an adjacent block A1, which is called a bottom-sideextension adjacent block.

Adjacent blocks bordering a top-side boundary of a partition block(prediction unit) are called top-side adjacent blocks. For the obliquelined, first prediction unit PU0 in the left-hand side of FIG. 3, B1belongs to the top-side adjacent blocks while, for the oblique lined,second prediction unit PU1 in the right-hand side of FIG. 3, B1 belongsto the top-side adjacent blocks. With respect to the oblique lined,first prediction unit PU0 in the left-hand side of FIG. 3, B0 is calleda right-hand side extension adjacent block bordering the right-hand sideboundary of a top-side adjacent block B1; meanwhile, with respect to theoblique lined, second prediction unit PU1 in the right-hand side of FIG.3, B0 is called a right-hand side extension adjacent block bordering theright-hand side boundary of a top-side adjacent block B1.

In the left-hand side of FIG. 3, in case of the oblique lined, firstprediction unit PU0, B2 borders on the left top-side edge of the firstprediction unit PU0 and B2 is called a left top-side adjacent block.

With reference to FIG. 3 again, for the oblique lined, first predictionunit PU0 in the left-hand side of FIG. 3, five adjacent blocks B2, B1,B0, A1, and A0 shown in the left-hand side of FIG. 3 are used ascandidate adjacent blocks for block merging, while, for the obliquelined, second prediction unit PU1 in the right-hand side of FIG. 3, fiveadjacent blocks B2, B1, B0, A1, and A0 shown in the right-hand side ofFIG. 3 are used as candidate adjacent blocks for block merging.

As shown in the right-hand side of FIG. 3, in case the five adjacentblocks B2, B1, B0, A1, and A0 are used as candidate adjacent blocks forblock merging with respect to the second prediction unit PU1, the motionparameters of the left-hand side adjacent block A1 cannot be obtaineduntil the motion parameters of the first prediction unit PU0 arereconstructed.

Therefore, as shown in FIG. 3, a process of constructing a list ofmerging candidate blocks for block merging of the first prediction unitPU0 is first performed and encoding (or decoding) of the firstprediction unit is performed and a process of constructing a list ofmerging candidate blocks for block merging of the second prediction unitPU1 and subsequently encoding (or decoding) of the second predictionunit PU1 is performed.

As a result, it is impossible to carry out parallel processing of theprocess of constructing a list of merging candidate blocks for blockmerging of the first prediction unit PU0 and the process of constructinga list of merging candidate blocks for block merging of the secondprediction unit PU1.

In what follows, described will be a method for carrying out parallelprocessing of block merging and an encoding (or decoding) operation forasymmetrically partitioned prediction units according to the exampleembodiments of the present invention.

FIGS. 5 to 7 illustrate common merging candidate blocks enablingparallel processing of prediction units PU0, PU1 partitionedasymmetrically according to example embodiments of the presentinvention. FIG. 8 illustrates a process where block merging of twopartitioned blocks in a parallel fashion and an encoding (or decoding)operation are performed.

First, with reference to FIGS. 5 and 7, a 2N×2N coding unit (CU) issplit into partitions consisting of a partition block PU0 (predictionunit) having size of nL×2N (where nL is 2N×¼) and a partition block PU1(prediction unit) having size of nR×2N (where nR is 2N×¾). In whatfollows, PU0 of FIGS. 5 to 7 is called a first prediction unit while PU1is called a second prediction unit. Here, size of a coding unit (CU) is2N×2N (where N is a positive integer) and N can be one of 2, 4, 8, 16,and 32. A technique of utilizing common merging candidate blocks toenable parallel processing of asymmetrically partitioned predictionunits PU0 and PU1 can be applied to all of coding units where N can takea value from among 2, 4, 8, 16, and 32 or can be applied to the codingunits where N can assume only one particular value—for example, one fromamong 2, 4, 8, 15, and 32. In case the largest coding unit (LCU) is64×64, the smaller the size of the coding unit (CU), the larger becomesthe number of constructing a list of common merging blocks includingcommon merging candidate blocks for the entire 64×64 block; in thiscase, if the common merging candidate list is applied for the case wheresize of the coding unit (CU) is small rather than the case where size ofthe coding unit (CU) is large, the number of constructing the commonmerging candidate list can be significantly reduced, thereby reducingcomplexity. Meanwhile, if parallel processing is performed by applyingmuch more of the common merging list, performance loss becomes large.Therefore, by taking account both of performance loss and complexity, ifthe minimum size of a prediction unit (PU) is 4×4, for example,complexity can be reduced a lot without sacrificing performancesignificantly by employing the common merging candidate blocks only forthe case where size of the coding unit (CU) is 8×8 (the smallest number4 excluding 2 is selected from the N values of 2, 4, 8, 16, and 32).

Meanwhile, the largest coding unit can be split into a plurality ofnon-overlapping motion estimation regions (or merge estimation regions);motion estimation can be made to be performed sequentially among motionestimation regions within the largest coding unit (LCU) whereas all theprediction units (PUs) belonging to one motion estimation region withinthe largest coding unit (LCU) can be made to perform motion estimationin a parallel fashion. Here, size of the motion estimation region issmaller than that of the LCU and the motion estimation region can have asquare shape.

Depending on size of a motion estimation region, it can be determinedwhether to allow parallel processing of prediction units (PUs) withinthe motion estimation region by using common merging candidate blocks.For example, suppose size of the smallest prediction unit is 4×4. Ifsize of the motion estimation region is 4×4, a sequential mergingoperation is applied to all the prediction units within the largestcoding unit (LCU). Meanwhile, it can be made such that parallelmerging—a technique using common merging candidate blocks to enableparallel processing—is allowed for all the prediction units (PUs) withinthe motion estimation region only when the size of the motion estimationregion is 8×8 or more.

Depending on size of the motion estimation region as described above, apredetermined value can be included in a PPS (Picture Parameter Set) andtransmitted from an encoder to a decoder to indicate possibility of theparallel merging depending on the size of the motion estimation region.The predetermined value can take one of 0, 1, 2, 3, and 4, for example;size of the motion estimation region for each of the predeterminedvalues 0, 1, 2, 3, and 4 can be 4×4, 8×8, 16×16, 32×32, and 64×64,respectively.

If a current prediction unit (PU) and an adjacent prediction unit (PU)belong to the same motion estimation region (in other words, within thesame motion estimation region), the corresponding adjacent predictionunit is marked as non-available whereas the current prediction unit andthe adjacent prediction unit belong to motion estimation regionsdifferent from each other, the corresponding adjacent prediction unit ismarked as available; thus, availability of the list of common mergingcandidate blocks for motion vector estimation can be determined. In casepart of common merging candidate blocks adjacent to a current codingunit (CU) having size of 8×8 (adjacent prediction units) is notavailable, the merging operation described above can be performed byusing adjacent common merging candidate blocks available.

For the asymmetrically partitioned, first PU0 and the second predictionunit PU1 shown in FIGS. 5 to 7 according to example embodiments of thepresent invention, block merging and an encoding (or decoding) operationare processed in a parallel fashion for the first PU0 and the secondprediction unit PU1 by using common merging candidate blocks.

Referring to FIG. 5, the common merging candidate blocks for the firstPU0 530 and the second prediction unit PU1 550 may include LT, LB1, LB0,RT1, RT0, CT1, and CT2 block. In other words, the list of mergingcandidate blocks for the first prediction unit PU0 530 includes LT, LB1,LB0, RT1, RT0, CT1, and CT2 block while the list of merging candidateblocks of the second prediction unit PU1 550 includes LT, LB1, LB0, RT1,RT0, CT1, and CT2 block.

The LT1 block is a left-top side adjacent block of the first predictionunit PU0 530; the LB1 block is the bottom-most, left-hand side blocklocated at the lowest position of left-hand side blocks of the firstprediction unit PU0; the LB0 block is a lower-side extension adjacentblock bordering on the lower-side boundary of the bottom-most, left-handside adjacent block LB1 of the first prediction unit. The RT1 block isthe rightmost, upper-side adjacent block located at the rightmostposition of lower-side adjacent blocks (CT2, . . . , RT1) of the secondprediction unit PU1 550; RT0 block is a right-hand side extensionadjacent block bordering on the right-side boundary of the rightmost,upper-side adjacent block RT1. Among upper-side adjacent blocks of thefirst PU0 and the second prediction unit PU1, the CT1 and the CT2 blockare upper-side, central adjacent blocks located in the left-hand andright-hand side of an extension of a central line formed whenun-partitioned prediction unit PU is split into halves in verticaldirection. Here, the CT1 block which is an upper-side adjacent block andbordering on the central line between the first prediction unit PU0 andthe second prediction unit PU1 in the left-hand side is defined as afirst upper-side central adjacent block while the CT2 block which is anupper-side adjacent block and bordering on the central line between thefirst prediction unit PU0 and the second prediction unit PU1 in theright-hand side is defined as a second upper-side central adjacentblock.

The list of merging candidate blocks of the first prediction unit PU0530 includes seven blocks: LT, LB1, LB0, RT1, RT0, CT1, and CT2. Thelist of merging candidate blocks of the second prediction unit PU1 550includes the same seven blocks: LT, LB1, LB0, RT1, RT0, CT1, and CT2.Also, the LT, LB1, LB0, RT1, RT0, CT1, and CT2 block included in thelist of merging candidate blocks of the second prediction unit PU1 550includes only adjacent blocks which can be constructed even beforereconstructing motion parameters of the first prediction unit PU0.

Also, since LT, LB1, LB0, CT1, and CT2 block among common mergingcandidate blocks coincide with the candidate merging blocks of the firstprediction unit PU0 of FIG. 3, the same performance can be actuallysecured compared with a case where block merging of the first predictionunit PU0 is applied.

Therefore, as shown in FIG. 8, a first process constructing a list ofmerging candidate blocks (LT, LB1, LB0, RT1, RT0, CT1, and CT2 block)for block merging of the first prediction unit PU0 and a second processconstructing a list of merging candidate blocks (LT, LB1, LB0, RT1, RT0,CT1, and CT2 block) for block merging of the second prediction unit PU1are not performed separately but can be performed as a single process810 constructing a single common merging candidate block; and anencoding (or decoding) process 830 for the second prediction unit PU1can be performed in parallel with the encoding (or decoding) process 820for the first prediction unit PU1, thereby reducing encoding timeconsiderably.

The common merging candidate blocks can be predetermined beforehandaccording to a rule between an encoder and a decoder; in this case,information about the common merging candidate blocks doesn't have to betransmitted from the encoder to the decoder.

FIG. 6 illustrates common merging candidate blocks enabling parallelprocessing of prediction units PU0, PU1 partitioned asymmetricallyaccording to another example embodiment of the present invention.

As shown in FIG. 6, the list of common merging candidate blocks includeseven blocks of LT 601, LB1 611, LB0 613, RT1 607, RT0 609, ET1 603, ET2605. Different from FIG. 4, the first upper-side central adjacent blockCT1 and the second upper-side central adjacent block CT2 are in thelist; instead ET1 and ET2 are newly included in the list, which isdifferent from the example embodiment of FIG. 5.

Since the remaining LT, LB1, LB0, RT1, and RT0 block are the same asFIG. 5, detailed descriptions will be omitted.

Among upper-side adjacent blocks of the first PU0 and the secondprediction unit PU1, the ET1 and ET2 block are upper-side centraladjacent blocks located in the left-hand and right-hand side of anextension of a boundary line (which corresponds to a line dividing anon-partitioned prediction unit (PU) into a quarter in verticaldirection) between the first PU0 and the second prediction unit PU1.Here, The ET1 block, which is an upper-side adjacent block and borderingon the boundary line between the first PU0 and the second predictionunit PU1 in the left-hand side is defined as a first upper-sideedge-adjacent block while the ET2 block, which is an upper-side adjacentblock and bordering on the boundary line between the first PU0 and thesecond prediction unit PU1 in the right-hand side is defined as a secondupper-side edge-adjacent block. In other words, the ET1 block is therightmost, upper-side adjacent block located at the rightmost positionamong upper-side adjacent blocks (LT, . . . , ET1) of the firstprediction unit PU0 while the ET2 block is the leftmost, upper-sideadjacent block located at the leftmost position among upper-sideadjacent blocks (ET2, . . . , RT1) of the second prediction unit PU1.

Also, in a yet another example embodiment of the present invention, incase a 2N×2N coding unit (CU) is partitioned in vertical direction intoa partition block PU0 (prediction unit) having size of nL×2N (where nLis 2N×¾) and a partition block PU1 (prediction unit) having size ofnR×2N (where nR is 2N×¼), common merging candidate blocks can beconstructed as shown in FIG. 7.

Referring to FIG. 7, the common merging candidate blocks for the firstPU0 730 and the second prediction unit PU1 750 may include LT, LB1, LB0,RT1, RT0, ET1, and ET2 block. In other words, the list of mergingcandidate blocks of the first prediction unit PU0 730 includes LT, LB1,LB0, RT1, RT0, ET1, and ET2 block while the list of merging candidateblocks of the second prediction unit PU1 750 includes LT, LB1, LB0, RT1,RT0, ET1, and ET2 block.

The LT1 block is a left-top side adjacent block of the first predictionunit PU0 530; the LB1 block is the bottom-most, left-hand side blocklocated at the lowest position of left-hand side blocks of the firstprediction unit PU0; the LB0 block is a lower-side extension adjacentblock bordering on the lower-side boundary of the bottom-most, left-handside adjacent block LB1 of the first prediction unit. The RT1 block isthe rightmost, upper-side adjacent block located at the rightmostposition of lower-side adjacent blocks (ET2, . . . , RT1) of the secondprediction unit PU1 750; The RT0 block is a right-hand side extensionadjacent block bordering on the right-side boundary of the rightmost,upper-side adjacent block RT1. The ET1 and ET2 block are upper-sidecentral adjacent blocks located in the left and right-hand side of anextension of a boundary line (which corresponds to a line dividing anon-partitioned prediction unit (PU) into three fourths in verticaldirection) between the first PU0 and the second prediction unit PU1among upper-side adjacent blocks of the first PU0 and the secondprediction unit PU1. Here, the ET1 block, which is an upper-sideadjacent block bordering on the boundary line between the first PU0 andthe second prediction unit PU1 in the left-hand side, is defined as afirst upper-side edge-adjacent block while the ET2 block, which is anupper-side adjacent block bordering on the boundary line between thefirst PU0 and the second prediction unit PU1 in the right-hand side, isdefined as a second upper-side edge-adjacent block. In other words, theET1 block is the rightmost, upper-side adjacent block located in therightmost position among upper-side adjacent blocks (LT, . . . , ET1) ofthe first prediction unit PU0 while the ET2 block is the leftmost,upper-side adjacent block located at the leftmost position amongupper-side adjacent blocks (ET2, . . . , RT1) of the second predictionunit PU1.

The list of merging candidate blocks of the first prediction unit PU0730 includes seven blocks: LT, LB1, LB0, RT1, RT0, ET1, and ET2. Thelist of merging candidate blocks of the second prediction unit PU1 750includes the same seven blocks: LT, LB1, LB0, RT1, RT0, ET1, and ET2.Also, the LT, LB1, LB0, RT1, RT0, ET1, and ET2 block included in thelist of merging candidate blocks of the second prediction unit PU1 750includes only adjacent blocks which can be constructed even beforereconstructing motion parameters of the first prediction unit PU0.

Therefore, as shown in FIG. 8, a first process constructing a list ofmerging candidate blocks (LT, LB1, LB0, RT1, RT0, ET1, and ET2 block)for block merging of the first prediction unit PU0 and a second processconstructing a list of merging candidate blocks (LT, LB1, LB0, RT1, RT0,ET1, and ET2 block) for block merging of the second prediction unit PU0are not performed separately but can be performed as a process 810constructing a first common merging candidate block; and an encoding (ordecoding) process 830 for the second prediction unit PU1 can beperformed in parallel with the encoding (or decoding) process 820 forthe first prediction unit PU1, thereby reducing encoding timeconsiderably.

Although not shown in the figure, in case of asymmetric partitioninginto the first PU0 and the second prediction unit PU1 along verticaldirection, particular candidate blocks (at least one from among LB0,ET1, ET2, RT0 and RT1) may be omitted from among the seven commonmerging candidate blocks.

Although the list of common merging candidate blocks in FIGS. 5 to 7contains seven blocks, the number of blocks included in the list ofcommon merging candidate blocks is not limited to the above example andthe list can be constructed only with six, five, or four candidateblocks.

As described above, in case a set of common merging candidate blocks isconstructed, a block having motion parameter similar to that of acurrent block (prediction unit) is selected from among the mergingcandidate blocks and the selected merging candidate block and thecurrent block are merged into one. Selection of a block having motionparameter similar to that of the current block (prediction unit) isperformed if the difference between the motion parameter of the currentblock (prediction unit) and that of each of merging candidate blocksfrom the set of merging candidate blocks is smaller than a predeterminedthreshold value.

The same motion parameter is applied to the current block and theselected merging candidate block and the same motion parameter istransmitted to a decoder.

In case the current block is merged with the selected merging candidateblock, information of the merged block is transmitted to the decoderwithout transmitting motion parameter of the current block to thedecoder and the decoder can decode the current block by using theinformation of the merged block and the motion parameter ofalready-decoded merged block.

As described in the example embodiment above, in case the first PU0 andthe second prediction unit PU1 include adjacent blocks of the first PU0and the second prediction unit PU1 as spatial merging candidate blocks,the first PU0 and the second prediction unit PU1 can include commonspatial merging candidate blocks for all the possible partition typesirrespective of a partition type and indices of a coding unit having apredetermined size.

In the previous example embodiment, described was an example where thelist of common merging candidate blocks includes spatial mergingcandidate blocks comprised of adjacent blocks of the first PU0 and thesecond prediction unit PU1; in another example embodiment of the presentinvention, temporal merging candidate block may be further incorporatedinto the list of common merging candidate blocks.

In case the first PU0 and the second prediction unit PU1 includetemporal merging candidate block as common merging candidate block, thefirst PU0 and the second prediction unit PU1 of a coding unit (CU) mayuse a reference picture index of a block, at a predetermined particularposition, among the spatial common merging candidate blocks as areference picture index for temporal motion vector prediction (MVP) oftemporal merging candidate block. Here, in case of temporal motionvector prediction, a motion vector and a reference picture index aretransmitted to the decoder. Here, the block at the predeterminedparticular position can be rendered executable through parallelprocessing by using previously encoded adjacent blocks which can beconstructed even before reconstructing motion parameters of a first PU0and a second prediction unit PU1 from among blocks included in the listof common merging candidate blocks.

Also, the temporal merging candidate block may further be includedco-located block, which is included in the previous picture of a currentpicture and corresponds to a current prediction unit (PU), in the listof common merging candidate list.

FIG. 9 is a block diagram of a video encoding apparatus using blockmerging according to one example embodiment of the present invention.

With reference to FIG. 9, a video encoding apparatus includes a encoder530 and the encoder 530 includes an inter prediction unit 532, an intraprediction unit 535, a subtractor 537, a transform unit 539, aquantization unit 541, an entropy encoding unit 543, an inversequantization unit 545, an inverse transform unit 547, an adder 549, anda frame buffer 551. The inter prediction unit 532 includes a motionprediction unit 531 and a motion compensation unit 533.

The encoder 530 performs encoding of an input video. The input video canbe used on a prediction unit (PU) basis for inter prediction in theinter prediction unit 532 or intra prediction in the intra predictionunit 535.

The encoder 530 performs encoding for prediction units.

The inter prediction unit 532 splits a currently provided predictionunit to be encoded into partitions by using a partitioning method andgenerates a motion vector by estimating the motion on a partitionedblock basis.

The motion prediction unit 531 splits a currently provided predictionunit to be encoded into partitions by using a partitioning method andfor each partitioned block, a motion vector is generated on a blockbasis by searching at least one reference picture (which is stored in aframe buffer after encoding is completed) located before and/or after acurrent encoding picture for a region similar to a current encodingpartitioned block. Here, size of a block used for the motion estimationcan be varied.

The motion compensation unit 533 generates a prediction block (orpredicted prediction unit) obtained by executing motion compensation byusing a motion vector generated from the motion prediction unit 531 andthe reference picture.

The inter prediction unit 532 obtains motion parameters for each mergedblock by carrying out the block merging described above.

In other words, the inter prediction unit 532 constructs a list ofcommon merging candidate blocks including a predetermined number ofcommon merging candidate blocks selected from among blocks adjacent to acurrent coding unit asymmetrically partitioned into a first and a secondprediction unit as described above; and selects at least one candidateblock from the list of common merging candidate blocks for each of thefirst and the second prediction unit.

The inter prediction unit 532 obtains motion parameters of blocks mergedwith the current coding unit by using the at least one common mergingcandidate block selected. Motion parameters for each block merged bycarrying out the block merging above are transmitted to the decoder.

The intra prediction unit 535 performs intra prediction encoding byusing pixel correlation between blocks. The intra prediction unit 535performs intra prediction which obtains a prediction block of a currentprediction unit by predicting pixel values from pre-encoded pixel valuesof a block within a current frame (or picture).

The subtractor 537 generates residues from a prediction block (orpredicted prediction unit) provided by the motion compensation unit 533by subtracting the current block (or current prediction unit); thetransform unit 539 and the quantization unit 541 apply DCT (DiscreteCosine Transform) to the residues and quantize the transformed residues.Here, the transform unit 539 can carry out transformation based oninformation about size of a prediction unit; for example, the transformunit 539 can carry out transformation by using a maximum of 32×32 or64×64 pixel block. Also, the transform unit 539 can performtransformation on a particular transform unit (TU) basis independent ofthe prediction unit size information provided from the prediction unitdetermination unit 510. For example, the transform unit (TU) may take aminimum of 4×4 pixel block to a maximum of 32×32 pixel block. Also, themaximum size of the transform unit (TU) may exceed a 32×32 pixelblock—for example, a 64×64 pixel block. The transform unit sizeinformation may be included in information about a transform unit andthus transmitted to the decoder.

The entropy encoding unit 543 generates a bit stream by applying entropyencoding to header information including quantized DCT coefficients,motion vector, determined prediction unit information, partitioninformation, transform unit information, and so on.

The inverse quantization unit 545 inversely quantizes the data quantizedthrough the quantization unit 541 and the inverse transform unit 547inversely transforms the inversely quantized data. The adder 549reconstructs a video by adding the inversely transformed data and apredicted prediction unit provided by the motion compensation unit 533and provides the reconstructed video to the frame buffer 551; the framebuffer 551 stores the reconstructed video.

FIG. 10 is a flow diagram illustrating a video encoding method usingblock merging according to one example embodiment of the presentinvention.

With reference to FIG. 10, first, if a input video is provided to anencoding apparatus (Step 610), coding units of the input video are splitinto partitions by using a partitioning method; for each partitionedblock, a motion vector is generated on a block basis by searching atleast one reference picture (which is stored in the frame buffer 551after encoding is completed) located before and/or after a currentencoding picture for a region similar to a current encoding partitionedblock; prediction blocks (or predicted prediction units) are generatedby carrying out motion compensation by using the generated motion vectorand the reference picture (Step 620).

Next, the encoding apparatus generates motion parameters for each ofmerged blocks by carrying out block merging described above for thepartitioned prediction units (PUs) (Step 630). Motion parameters for therespective blocks merged by carrying out the block merging describedabove are transmitted to the decoder.

The encoding apparatus obtains a difference between a current predictionunit and the predicted prediction unit and generates residues (Step640).

Next, the encoding apparatus transforms the generated residues andquantizes the transformed residues (Step 650); a bit stream is generatedby applying entropy encoding to the header information includingquantized DCT coefficients, motion parameters, and so on. (Step 660).

A video encoding apparatus and a video encoding method by using blockmerging according to example embodiments of the present inventiontransmits motion parameter only once for the whole blocks merged byblock merging rather than transmit respective motion parameter for eachof asymmetrically partitioned blocks (prediction units). In this way,since the amount of transmission for motion parameters is reduced,encoding efficiency of video having resolution more than HD or UHD(Ultra High Definition) resolution can be improved.

A video decoding apparatus and a video decoding method by using blockmerging according to example embodiments of the present inventionreconstructs a motion vector of a block-merged block by using motionparameter of the block-merged block transmitted from the encodingapparatus described above; a motion prediction unit generates a motionvector on a block basis and the motion compensation unit performs motioncompensation by using the motion vector generated by the motionprediction unit and a reference picture.

The video decoding apparatus includes a decoder and the decoder includesan inter prediction unit and an intra prediction unit. The remainingcomponents of the decoder are well-known to the public; therefore,detailed description thereof will be omitted. The inter prediction unitincludes a motion prediction unit and a motion compensation unit.

In the same way as the encoding apparatus, the inter prediction unitconstructs a list of common merging candidate blocks including apredetermined number of common merging candidate blocks selected fromblocks adjacent to a current coding unit, which have been asymmetricallypartitioned into a first and a second prediction unit, the interprediction unit generates a motion vector on a block basis byreconstructing motion parameters of a block-merged block by using atleast one candidate block selected from the list of common mergingcandidate blocks for each of the first and the second prediction unit,and the inter prediction unit performs motion compensation by using thegenerated motion vector and a reference picture.

In case of a video decoding apparatus and a video decoding method whichuses the block merging, size of a coding unit (CU) is 2N×2N (where N isa positive integer) and N can be one of 2, 4, 8, 16, and 32. A techniqueof utilizing common merging candidate blocks to enable parallelprocessing of asymmetrically partitioned prediction units PU0 and PU1can be applied to all of coding units where N can take a value fromamong 2, 4, 8, 16, and 32 or can be applied to the coding units where Ncan assume only one particular value—for example, one from among 2, 4,8, 15, and 32. In case the largest coding unit (LCU) is 64×64, thesmaller the size of the coding unit (CU), the larger becomes the numberof constructing a list of common merging blocks including common mergingcandidate blocks for the entire 64×64 block; in this case, if the commonmerging candidate list is applied for the case where size of the codingunit (CU) is small rather than the case where size of the coding unit(CU) is large, the number of constructing the common merging candidatelist can be significantly reduced, thereby reducing complexity.Meanwhile, if parallel processing is performed by applying much more ofthe common merging list, performance loss becomes large. Therefore, bytaking account both of performance loss and complexity, if the minimumsize of a prediction unit (PU) is 4×4, for example, complexity can bereduced a lot without sacrificing performance significantly by employingthe common merging candidate blocks only for the case where size of thecoding unit (CU) is 8×8 (the smallest number 4 excluding 2 is selectedfrom the N values of 2, 4, 8, 16, and 32).

Meanwhile, the largest coding unit (LCU) can be split into a pluralityof non-overlapping motion estimation regions (or merge estimationregions); motion estimation can be made to be performed sequentiallyamong motion estimation regions within the largest coding unit (LCU)whereas all the prediction units (PUs) belonging to one motionestimation region within the largest coding unit (LCU) can be made toperform motion estimation in a parallel fashion. For example, size ofthe motion estimation region may be smaller than that of the LCU and themotion estimation region can have a square shape.

Depending on size of a motion estimation region, it is determinedwhether to allow parallel processing of prediction units (PUs) withinthe motion estimation region by using common merging candidate blocks.For example, suppose size of the smallest prediction unit is 4×4. Ifsize of the motion estimation region is 4×4, a sequential mergingoperation is applied to all the prediction units within the largestcoding unit (LCU). Meanwhile, it can be made such that parallelmerging—a technique using common merging candidate blocks to enableparallel processing—is allowed for all the prediction units (PUs) withinthe motion estimation region only when the size of the motion estimationregion is 8×8 or more.

If a current prediction unit (PU) and an adjacent prediction unit (PU)belong to the same motion estimation region (in other words, within thesame motion estimation region), the corresponding adjacent predictionunit is marked as non-available whereas the current prediction unit andthe adjacent prediction unit belong to motion estimation regionsdifferent from each other, the corresponding adjacent prediction unit ismarked as available; thus, availability of the list of common mergingcandidate blocks for motion vector estimation can be determined. In casepart of common merging candidate blocks adjacent to a current codingunit (CU) having size of 8×8 (adjacent prediction units) is notavailable, the merging operation described above can be performed byusing adjacent common merging candidate blocks available.

As described in the encoding apparatus above, in case the first PU0 andthe second prediction unit PU1 include adjacent blocks of the first PU0and the second prediction unit PU1 as spatial merging candidate blocks,the first PU0 and the second prediction unit PU1 can include commonspatial merging candidate blocks for all the possible partition typesirrespective of a partition type and indices of a coding unit having apredetermined size.

In the same way as the encoding apparatus, the list of common mergingcandidate blocks includes spatial merging candidate blocks comprised ofadjacent blocks of the first PU0 and the second prediction unit PU1. Inaddition, temporal merging candidate block may be further incorporatedinto the list of common merging candidate blocks.

In case the first PU0 and the second prediction unit PU1 includetemporal merging candidate block as common merging candidate blocks, thefirst PU0 and the second prediction unit PU1 of a coding unit (CU) mayuse a reference picture index of a block, at a predetermined particularposition, among the spatial common merging candidate blocks as areference picture index for temporal motion vector prediction (MVP) oftemporal merging candidate blocks. Here, the block at the predeterminedparticular position can be rendered executable through parallelprocessing by using previously encoded adjacent blocks which can beconstructed even before reconstructing motion parameters of a first PU0and a second prediction unit PU1 from among blocks included in the listof common merging candidate blocks.

According to methods for encoding/decoding of a video by using blockmerging as described above, a current block is asymmetricallypartitioned to generate a first and a second prediction unit. For eachof the first and the second prediction unit, motion parameter(s) are nottransmitted but a list of common merging candidate blocks including apredetermined number of common merging candidate blocks selected fromblocks adjacent to the current block is constructed. At least one commonmerging candidate block selected from among common merging candidateblocks belonging to the list of common merging candidate blockstransmits motion parameter(s) only once for the current block and thewhole blocks merged. In this way, since the amount of transmission ofside information such as the motion parameter is reduced, encodingefficiency of a video of more than HD or UHD (Ultra High Definition)resolution can be improved.

A first process constructing a list of merging candidate blocks forblock merging of a first prediction unit PU0 generated from asymmetricpartition and a second process constructing a list of merging candidateblocks for block merging of a second prediction unit PU1 are notperformed separately but can be performed in the form of a singleprocess constituting the common merging candidate block. Since anencoding (or decoding) process for the second prediction unit PU1 can beperformed in parallel with an encoding (or decoding) process for thefirst prediction unit PU0, encoding time can be reduced considerably.

What is claimed is:
 1. A video encoding method, comprising: constructinga list of common merging candidate blocks by including a predeterminednumber of the common merging candidate blocks selected from amongadjacent blocks of a current coding unit, the current coding unitpartitioned into a first prediction unit and a second prediction unit;selecting at least one common merging candidate block from among thelist of common merging candidate blocks for each of the first predictionunit and the second prediction unit; and sending correspondinginformation of the selected at least one common merging candidate blockto a decoder for each of the first prediction unit and the secondprediction unit, wherein the constructing of the list of common mergingcandidate blocks is performed only when a size of the current codingunit is 8-by-8.
 2. The video encoding method of claim 1, wherein theselected at least one common merging candidate block for the secondprediction unit comprises adjacent blocks which are constructed beforereconstructing a motion parameter of the first prediction unit.
 3. Thevideo encoding method of claim 1, wherein a parallel merging for thefirst prediction unit and the second prediction unit within a motionestimation region is allowed only when a size of the motion estimationregion is larger than a predetermined size.
 4. The video encoding methodof claim 1, wherein a largest coding unit (LCU) is divided into aplurality of non-overlapping motion estimation regions, motionestimation is performed sequentially on the motion estimation regionswithin the largest coding unit (LCU), and the motion estimation isperformed in a parallel fashion for the first prediction unit and thesecond prediction unit belonging to a motion estimation region withinthe largest coding unit (LCU).
 5. The video encoding method of claim 4,wherein in case both the current prediction unit and another predictionunit adjacent to the current prediction unit belong to the same motionestimation region, said another prediction unit is denoted asnon-available, and in case the current prediction unit and said anotherprediction unit adjacent to the current prediction unit belong to motionestimation regions different from each other, said another predictionunit is denoted as available.
 6. The video encoding method of claim 1,wherein the first prediction unit and the second prediction unit withinthe current coding unit utilize a reference picture index of a block, ata predetermined particular position, from among spatial common mergingcandidate blocks as a reference picture index for temporal motion vectorprediction (MVP) of a temporal merging candidate block.
 7. The videoencoding method of claim 6, wherein the block, at the predeterminedparticular position, uses a previously encoded adjacent block which isconstructed before reconstructing a motion parameter of the firstprediction unit and the second prediction unit from among blocksincluded in the list of common merging candidate blocks.
 8. A videoencoding apparatus, comprising: an inter prediction unit configured toconstruct a list of common merging candidate blocks by including apredetermined number of common merging candidate blocks selected fromblocks adjacent to a current coding unit, the current coding unitpartitioned into a first prediction unit and a second prediction unit,and select at least one common merging candidate block from the list ofcommon merging candidate blocks for each of the first prediction unitand the second prediction unit, wherein the inter prediction unit isconfigured to construct the list of common merging candidate blocks onlywhen a size of the current coding unit is 8-by-8.
 9. A video decodingapparatus, comprising: an inter prediction unit configured to constructa list of common merging candidate blocks by including a predeterminednumber of common merging candidate blocks selected from blocks adjacentto a current coding unit, the current coding unit partitioned into afirst prediction unit and a second prediction unit, generate a motionvector by reconstructing a motion parameter of a block-merged block byusing at least one common merging candidate block selected from the listof common merging candidate blocks for each of the first and the secondprediction unit, and perform motion compensation by using the generatedmotion vector and a reference picture, wherein the inter prediction unitis configured to construct the list of common merging candidate blocksonly when a size of the current coding unit is 8-by-8.